JP2019204700A - Fuel cell manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a fuel cell having a catalyst layer in which a catalyst supported in pores of a carbon support is coated with an ionomer by a simple treatment. A method of manufacturing a fuel cell is a method of manufacturing a fuel cell having electrodes on both sides of an electrolyte membrane, wherein the electrodes have a carbon support having pores, a catalyst and a catalyst layer containing an ionomer. A voltage is applied to the ink for the catalyst layer in which the carbon carrier, the catalyst and the ionomer and the solvent are mixed, or the catalyst layer formed by using the ink for the catalyst layer, the catalyst being in a semi-dried state Applying a voltage to the fuel cell having a layer. [Selection diagram] Figure 2

Description

  The present invention relates to a method for manufacturing a fuel cell. In particular, the present invention relates to a method for producing a solid polymer electrolyte fuel cell.

  The electrode reaction of a fuel cell is considered to occur at an electrolyte-catalyst-reactive gas (hydrogen) interface, which is called a three-phase interface. For this reason, in order to improve the power generation performance of the fuel cell, it is effective to have many three-phase interfaces in the catalyst layer. Therefore, conventionally, in the field of fuel cells, attempts have been made to improve the power generation performance of the fuel cells by focusing on the catalyst layer.

  In order to improve the power generation performance of the fuel cell, for example, a carrier having fine pores is hydrophilized using nitric acid, and the electrolyte similar to the electrolyte membrane (used in the catalyst layer) is used in the pores of the carrier. There has been reported a catalyst layer in which an electrolyte (hereinafter referred to as ionomer) is infiltrated (see, for example, Patent Document 1). The catalyst supported in the pores of the carrier is coated with an ionomer to form a three-phase interface not only on the surface of the carrier but also in the pores, thereby improving power generation performance.

JP 2017-126514 A

  However, since the hydrophilization treatment for producing the catalyst layer in which the ionomer is infiltrated into the pores of the carrier as described in Patent Document 1 is a liquid phase reaction treatment, washing treatment and drying are performed. Complicated post-processing such as processing is required. For this reason, there existed a subject that time required for manufacture became long and manufacturing cost raised.

  An object of the present invention is to provide a method for producing a fuel cell having a catalyst layer in which a catalyst supported in pores of a carbon support is coated with an ionomer by a simple treatment.

  A fuel cell manufacturing method according to the present invention is a fuel cell manufacturing method having electrodes on both surfaces of an electrolyte membrane, wherein the electrodes have a carbon layer having pores, a catalyst layer containing a catalyst and an ionomer. The catalyst is formed by applying a voltage to the ink for the catalyst layer obtained by mixing the carbon carrier, the catalyst, the ionomer and the solvent, or using the catalyst layer ink, and the catalyst is in a semi-dry state. Applying a voltage to the fuel cell having a layer.

  According to the present invention, it is possible to provide a method for producing a fuel cell having a catalyst layer in which a catalyst supported in the pores of a carbon support is coated with an ionomer by a simple treatment.

It is sectional drawing which shows an example of a structure of a fuel cell. It is sectional drawing which shows an example of the carbon support | carrier after the step which applies a voltage for demonstrating the manufacturing method of the fuel cell which concerns on this invention. It is sectional drawing which shows an example of the carbon support | carrier before the step which applies a voltage for demonstrating the manufacturing method of the fuel cell which concerns on this invention. 2 is a flowchart showing a method of manufacturing a fuel cell according to Embodiment 1 of the present invention. It is a flowchart which shows the manufacturing method of a fuel cell based on Embodiment 2 of this invention.

  Hereinafter, embodiments of the manufacturing method of the present invention will be described with reference to the drawings. The configuration described below is an example (representative example) as an embodiment of the present invention, and the present invention is not limited to the configuration described below.

  In the following, the same or similar descriptions are simplified or omitted as appropriate. It should be noted that the drawings are schematic and ratios of dimensions of the respective parts are different from actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(Fuel cell)
The fuel cell produced by the production method of the present invention may be a fuel cell having a single cell structure or a fuel cell having a stack structure.
FIG. 1 shows a configuration example of a fuel cell that is a basic unit of a fuel cell.

A fuel cell 10 shown in FIG. 1 is a solid polymer electrolyte fuel cell that generates electric power by receiving supply of hydrogen gas and oxygen gas. As shown in FIG. 1, the fuel cell 10 includes two separators 3 and a membrane electrode assembly 4 provided between the two separators 3. The separator 3 has a flow path for flowing the gas supplied to the fuel cell 10 to the membrane electrode assembly 4. When the fuel cell 10 has a stack structure, the separator 3 electrically connects adjacent cells.
As shown in FIG. 1, the membrane electrode assembly 4 includes an electrolyte membrane 1 and two electrodes 2.

  The electrolyte membrane 1 is a proton-donating solid polymer electrolyte membrane. For the electrolyte membrane 1, an electrolyte similar to the electrolyte that can be used in the electrode 2 described later can be used.

The two electrodes 2 are provided on both surfaces of the electrolyte membrane 1, respectively. One electrode 2 is an anode and is also called a fuel electrode. The other electrode 2 is a cathode and is also called an air electrode. In the electrode 2 that is an anode, a reaction in which electrons (e ⁻ ) and protons (H ⁺ ) are generated from the hydrogen gas (H ₂ ) supplied via the separator 3 occurs. Electrons move to the electrode 2 which is a cathode via an external circuit. This movement of electrons generates a current in the external circuit. Protons move in the electrolyte membrane 1 toward the electrode 2 which is a cathode. In the electrode 2 which is a cathode, oxygen gas (O ₂ ) is supplied through the separator 3, and oxygen ions (O ²⁻ ) are generated by electrons moving from the external circuit. The oxygen ions are combined with protons (2H ⁺ ) that have moved from the electrolyte membrane 1 to become water (H ₂ O).

  Each electrode 2 has a catalyst layer 21 and a gas diffusion layer 22 as shown in FIG. The gas diffusion layer 22 can be provided as necessary to diffuse the hydrogen gas or oxygen gas supplied to each electrode 2 to the electrode 2. As the gas diffusion layer 22, for example, a porous fiber sheet having conductivity, gas permeability and gas diffusibility such as carbon fiber, a porous metal plate such as a foam metal and an expanded metal can be used.

(Catalyst layer)
The catalyst layer 21 is provided adjacent to the electrolyte membrane 1. The catalyst layer 21 includes a catalyst, a carrier, and an ionomer, and promotes the above-described reaction of hydrogen gas and oxygen gas by the catalyst. In the catalyst layer 21, a particulate catalyst is supported on a carrier, and the carrier and the catalyst are covered with an ionomer. The support and the catalyst may be at least partially coated with an ionomer, but from the viewpoint of improving the catalyst utilization rate, it is preferable that the coated region is larger. From the viewpoint of increasing the reactivity with the gas, the ionomer layer covering the catalyst is preferably thin.

(catalyst)
The catalyst is not particularly limited as long as it has a catalytic action of hydrogen gas or oxygen gas. For example, platinum (Pt), ruthenium (Ru), iridium (Ir), rhodium (Rh), palladium (Pd), osmium ( Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (Co), nickel (Ni), manganese (Mn), vanadium (V), molybdenum (Mo), gallium ( Examples thereof include metals such as Ga) and aluminum (Al), mixtures of these metals, alloys, and the like. Of these, platinum, platinum-containing mixtures or alloys are preferable from the viewpoint of improving catalytic activity, poisoning resistance to carbon monoxide, heat resistance, and the like. When the catalyst is made of an alloy, the composition of the alloy depends on the type of metal to be alloyed, but the platinum content is 30 to 90 atomic% and the other metal contents are 10 to 70 atomic%. Can do.

The average particle diameter of the catalyst is not particularly limited, but is preferably 1 to 30 nm, more preferably 1 to 20 nm from the viewpoint of improving the catalyst utilization rate and the supportability on the carbon support.
The average particle diameter of the catalyst can be determined as the crystallite diameter determined from the half width of the diffraction peak of the catalyst particles in X-ray diffraction. The average particle diameter of the catalyst may be obtained as an average value of the particle diameters of n catalyst particles observed with a transmission electron microscope (TEM) or a scanning electron microscope (SEM). it can. n can be 200-300, for example.

(Carbon support)
As the carbon carrier, conductive porous carbon (mesoporous carbon or the like) having pores inside can be used. Examples of the porous carbon include carbon black such as ketjen black (registered trademark), acetylene black, and Vulcan (registered trademark), carbon having a structure in which a plurality of graphene sheets are laminated to form a mesoporous layer, and the like. .

The average particle size of the carbon support is not particularly limited, but is preferably 10 to 100 nm from the viewpoint of enhancing the supportability of the catalyst particles.
The average particle size of the carbon support can be determined by TEM or SEM. Specifically, in an image taken at an appropriate magnification (for example, 50,000 to 1,000,000 times) with TEM or SEM, the average value of the spherical n particle diameters is defined as the average particle diameter. n can be 200-300, for example.

  The average diameter, which is the average value of the diameters of the pores of the carbon support, is not particularly limited, but is preferably 2 to 20 nm from the viewpoint of supporting the catalyst particles in the pores. The average diameter of the pores of the carbon support is calculated by, for example, a nitrogen adsorption method.

The BET specific surface area of the carbon support is preferably 50 m ² / g or more, more preferably 500 m ² / g or more, and still more preferably 700 m ² / g or more, from the viewpoint of supporting many catalyst particles. On the other hand, BET specific surface area of the carbon support, from the viewpoint of uniformly support the catalyst particles is preferably 1500 m ² / g or less, more preferably 1300 m ² / g, more preferably 1000 m ² / g or less. Therefore, BET specific surface area of the carbon support preferably is 50~1500m ² / g, more preferably 500~1300m ² / g, more preferably 700~1000m ² / g.
The BET specific surface area of the carbon support is measured by a nitrogen adsorption method.

  The mass of the catalyst supported on the carbon support can be usually 1 to 99% by mass with respect to the total mass (100% by mass) of the catalyst and the carbon support, from the viewpoint of improving the catalyst activity and the supportability. 10-90 mass% is preferable, and 20-80 mass% is more preferable.

(Ionomer)
The ionomer is a proton-donating polymer electrolyte used in the catalyst layer 21. The ionomer has an acidic functional group with a polymer having a repeating structure as a main chain. The acidic functional group is not particularly limited as long as it is an acidic functional group, and examples thereof include a sulfonic acid group, a phosphoric acid group, and a carboxylic acid group. Among them, from the viewpoint of proton conductivity, a sulfonic acid group is preferable. As a mechanism of proton conduction by ionomers, a hydrophilic core is formed by an acidic functional group, and a network of clusters in which water molecules are localized is formed in the core. Proton moves through this hydrophilic network. Has been proposed.

  Examples of the ionomer that can be used for the catalyst layer 21 include ion-exchangeable polymers such as a fluorine-based polymer having an acidic functional group and a hydrocarbon-based polymer having an acidic functional group. The ionomer used for the catalyst layer 21 may be the same type as the electrolyte used in the electrolyte membrane 1 or may be a different type.

  A perfluorosulfonic acid polymer etc. are mentioned as a fluorine-type polymer which has an acidic functional group. The perfluorosulfonic acid polymer has a polytetrafluoroethylene (PTFE) unit and a perfluorosulfonic acid unit. A commercial item can also be used as a perfluorosulfonic acid polymer. Examples of commercially available products that can be used include Nafion (registered trademark, manufactured by DuPont), Aquivion (registered trademark, manufactured by Solvay), Flemion (registered trademark, manufactured by Asahi Glass), and Aciplex (registered). Trademark, manufactured by Asahi Kasei Co., Ltd.).

  Examples of the hydrocarbon polymer having an acidic functional group include an aromatic polymer having an acidic functional group and an aliphatic polymer having an acidic functional group.

  Examples of the aromatic polymer having an acidic functional group include sulfonated polyetheretherketone (SPEEK), sulfonated polyethersulfone (SPES), sulfonated polyphenylsulfone (SPPSU), sulfonated polyimide, and sulfonated polyetherimide. Sulfonated polysulfone, sulfonated polystyrene and the like.

  Examples of the aliphatic polymer having an acidic functional group include polyvinyl sulfonic acid and polyvinyl phosphoric acid.

  The ion exchange capacity (IEC) of the ionomer is preferably 0.6 meq / g or more, more preferably 0.9 meq / g or more, and 1.2 meq / g from the viewpoint of improving proton conductivity. More preferably g. The ion exchange capacity of the ionomer is preferably 3 meq / g, more preferably 2.5 meq / g or less, and further preferably 2 meq / g or less from the viewpoint of dimensional stability upon water absorption. Therefore, the ion exchange capacity of the ionomer is preferably 0.6 to 3 meq / g, more preferably 0.9 to 2.5 meq / g, and still more preferably 1.2 to 2 meq / g.

  When the carbon support is mesoporous carbon, the mass ratio (I / C) of the carbon support (C) to the ionomer (I) is preferably 0.1 or more, more preferably 0, from the viewpoint of enhancing ion conductivity. .2 or more, more preferably 0.3 or more. On the other hand, the mass ratio (I / C) is preferably 2 or less, more preferably 1.5 or less, and even more preferably 1 from the viewpoint of increasing the catalytic activity by suppressing the thickness of the ionomer covering the catalyst. .1 or less. Accordingly, the mass ratio is preferably 0.1 to 2, more preferably 0.2 to 1.5, and still more preferably 0.3 to 1.1.

  The thickness of the catalyst layer 21 is not particularly limited, but is preferably 0.1 μm or more and more preferably 1 μm or more from the viewpoint of the catalyst performance of the catalyst layer 21 and the formability of the catalyst layer 21. On the other hand, from the viewpoint of gas diffusibility, the thickness of the catalyst layer 21 is preferably 50 μm or less, and more preferably 20 μm or less. Therefore, the thickness of the catalyst layer 21 is preferably 0.1 to 50 μm, and more preferably 1 to 20 μm.

FIG. 2 is a cross-sectional view showing an example of the carbon carrier after the step of applying a voltage for explaining the method of manufacturing a fuel cell according to the present invention.
As shown in FIG. 2, the carbon support 12 has fine pores 14 inside, and has openings 15 of the pores 14 on the outer surface. The catalyst 11 is supported on the outer surface of the carbon support 12 and in the pores 14, and not only the catalyst 11 supported on the outer surface of the carbon support 12 but also the catalyst 11 supported in the pores 14 is covered with the ionomer 13. Has been.

  In the carbon support 12 after the step of applying a voltage, the opening 15 of the pore 14 is expanded, and the average diameter of the opening 15 of the pore 14 is larger than the average diameter of the pore 14. As a result, the ionomer 13 can enter the pores 14, and the catalyst 11 supported in the pores 14 is covered with the ionomer 13.

  The ratio of the average diameter of the openings 15 to the average diameter of the pores 14 is preferably 1.2 or more, more preferably 1 from the viewpoint of increasing the coverage of the ionomer 13 that covers the catalyst 11 in the pores 14. .3 or more, more preferably 1.4 or more. On the other hand, the ratio of the average diameter of the openings 15 to the average diameter of the pores 14 is usually 5.0 or less from the viewpoint of physical durability of the carbon support 12.

  The average diameter of the openings 15 of the pores 14 can be measured using a known method such as TEM or SEM. Specifically, in an image taken at an appropriate magnification (for example, 50,000 to 1,000,000 times) with a TEM or SEM, an average value of the diameters of the n openings 15 is defined as an average diameter. n can be 200-300, for example.

FIG. 3 is a cross-sectional view showing an example of the carbon carrier before the step of applying a voltage for explaining the fuel cell manufacturing method according to the present invention.
As shown in FIG. 3, the catalyst 11 supported in the pores 14 is not covered with the ionomer 13. Further, the opening 15 of the pore 14 is not expanded.

  As shown in FIG. 2, the carbon support 12 after the step of applying a voltage is also covered with the ionomer 13 in the catalyst 11 supported in the pores 14. For this reason, the fuel cell of one embodiment manufactured by the manufacturing method of the present invention including the step of applying a voltage has many three-phase interfaces in the catalyst layer, and is excellent in power generation performance.

(Fuel cell manufacturing method)
As an embodiment of the production method of the present invention, a method for producing a fuel cell in which the catalyst 11 supported in the pores 14 of the carbon support 12 is coated with an ionomer 13 will be described. The present embodiment is characterized by including a step of applying a voltage to the fuel cell having the catalyst layer ink or the semi-dry catalyst layer 21. By applying a voltage to the fuel for the catalyst layer ink or the fuel cell having the catalyst layer 21 in a semi-dry state, the outer surface of the carbon support 12 is mainly oxidized by the carbon oxidation reaction, and the average diameter of the openings 15 of the pores 14 is increased. growing. For this reason, it is possible to allow the ionomer 13 to enter the pores 14, and to obtain a fuel cell having the catalyst layer 21 in which the catalyst 11 supported in the pores 14 of the carbon support 12 is covered with the ionomer 13. it can.

  In this embodiment, since it is an electrooxidation method that oxidizes carbon by applying a voltage, a cleaning process, a drying process, and the like associated with the process are unnecessary. For this reason, in this embodiment, compared with the manufacturing method by the conventional liquid phase reaction, since the time required for manufacturing is short and simple and the manufacturing cost is low, it is suitable for continuous processing and large-scale manufacturing.

  With reference to FIG.4 and FIG.5, the step until obtaining a fuel cell is demonstrated as one Embodiment of the manufacturing method of this invention. FIG. 4 is a flowchart showing a manufacturing method according to Embodiment 1 of the present invention, including a step of applying a voltage to a fuel cell having a semi-dry catalyst layer. FIG. 5 is a flowchart showing a manufacturing method according to Embodiment 2 of the present invention, including the step of applying a voltage to the catalyst layer ink.

<Embodiment 1>
Below, the manufacturing method of the fuel cell based on Embodiment 1 is demonstrated.
As shown in FIG. 4, the fuel cell manufacturing method according to Embodiment 1 includes step S10, step S11, step S12, step S13, step S14, and step S15. Hereinafter, each step will be described.

(Step of supporting catalyst)
Step S <b> 10 is a step of supporting the catalyst 11 on the carbon support 12 having the pores 14.
The method for supporting the catalyst 11 on the carbon support 12 is not particularly limited, and a known method can be used. For example, when mesoporous carbon is used as the carbon support 12 and platinum is used as the catalyst 11, mesoporous carbon is dispersed in pure water, and nitric acid is added to the dispersion. Furthermore, after adding dinitrodiamine platinum salt aqueous solution, it reduces by adding ethanol and heating. Thereby, mesoporous carbon in which platinum particles are supported on the surface and inside the pores 14 is obtained. In addition, you may use the carbon support | carrier 12 with which the catalyst 11 was carry | supported already marketed.

(Step of preparing ink for catalyst layer)
Step S11 is a step of preparing an ink for a catalyst layer by mixing and stirring the ionomer 13 and a solvent containing water and an organic solvent, and further mixing and dispersing the carbon carrier 12 supporting the catalyst 11 to disperse. .

  Stirring is performed using, for example, a stirrer. The dispersion process is not particularly limited, and for example, the dispersion process is performed using a ball mill or the like. Here, the ball mill is a known device that rotates a ball and a material placed in a container and includes a bead mill. For example, a bead mill machine is filled with a mixed liquid of the carbon support 12 supporting the catalyst 11, the ionomer 13, and the solvent, and the dispersion treatment is performed. In the bead mill, dispersion is promoted by the movement of the beads accompanying the rotation of the rotating shaft, and an ink for the catalyst layer in which the catalyst 11 is coated with the ionomer 13 can be obtained. The material of the beads is not particularly limited, and examples thereof include ceramics, glass, and metal. The diameter of the beads is not particularly limited, but is usually 0.03 to 2 mm. Although the rotation speed of the base plate of the bead mill is not particularly limited, it is usually 100 to 1000 rpm. Although the rotation time of a bead mill is not specifically limited, Usually, it is 1 to 10 hours.

  The solvent includes water and an organic solvent, and is used as a dispersion medium when preparing the ink for the catalyst layer. Examples of water include tap water, pure water, ion exchange water, and distilled water. As an organic solvent, C1-C4 lower alcohols, such as cyclohexanol, methanol, ethanol, n-propanol, n-butanol, propylene glycol, benzene, toluene, xylene, etc. are mentioned, for example. In addition to these, for example, butyl acetate alcohol, dimethyl ether, ethylene glycol, or the like may be used as the organic solvent. These organic solvents may be used individually by 1 type, or may be used in the state of a 2 or more types of liquid mixture. The organic solvent is preferably methanol, ethanol, or n-propanol, which is an alcohol having a boiling point lower than that of water, from the viewpoint of ease of solvent removal. 2-Propanol is more preferable from the viewpoint of controlling to an appropriate drying rate.

  The mixing ratio of the ionomer 13 and the solvent is not particularly limited, but is usually ionomer: solvent = 1: 99 to 30:70. Although content of the water with respect to the whole solvent is not specifically limited, Usually, it is 5 mass% or more. Note that a commercially available ionomer dispersion may be used as the mixture of the ionomer 13 and the solvent.

(Step of forming a semi-dry catalyst layer)
In step S12, the catalyst layer ink is applied to the surface of the substrate selected from the electrolyte membrane 1, the resin sheet, the metal plate, and the like to form a coating film. This is a step of forming a catalyst layer 21 in a semi-dry state by leaving a part of the catalyst layer 21 in a semi-dry state.

  Here, the semi-dry state refers to a state in which part or all of the organic solvent in the coating film is removed by drying, but all of the water in the coating film is not removed. After the step of applying a voltage to be described later, the solvent in the coating film is completely removed by a drying treatment.

  A feature of the present invention is that the mean diameter of the openings 15 of the pores 14 in the carbon carrier 12 is expanded by including a voltage application step in the manufacturing step of the fuel cell, and the ionomer 13 is infiltrated into the pores 14. is there. When the solvent in the coating film is completely removed, even if the average diameter of the openings 15 of the pores 14 of the carbon support 12 is increased, the ionomer 13 penetrates into the pores 14 because the ionomer 13 does not have fluidity. Can not. For this reason, in the manufacturing method of Embodiment 1, in order to maintain the fluidity of the ionomer 13 in a high state, part or all of the organic solvent in the coating film is removed, but not all of the water is removed.

  The method for applying the ink for the catalyst layer to the surface of the substrate selected from the electrolyte membrane 1, resin sheet, metal plate, etc. is not particularly limited, but for example, screen printing, doctor blade method, spray coating method, etc. are used. Can do.

  Although the method of the drying process for making a coating film a semi-dry state is not specifically limited, For example, it can be made to dry by allowing a coating film to pass at predetermined temperature using a solvent dryer. The solvent dryer is, for example, a hot air drying furnace, but is not particularly limited as long as the solvent can be distilled off. For example, the solvent may be dried by radiant heat, or the solvent may be removed by both hot air and radiant heat. It may be dried. Although the drying temperature which is the atmospheric temperature in a solvent dryer will not be specifically limited if a coating film can be made into a semi-dry state, Usually, it is 20 to 100 degreeC. In addition, you may dry in inert gas atmosphere.

  In the catalyst layer 21 in the semi-dry state, the content of the organic solvent in the coating film is not particularly limited. For example, from the viewpoint of the fluidity of the ionomer 13, preferably 1 mass relative to the water in the coating film. % Or more, more preferably 2% by mass or more, and further preferably 3% by mass or more. On the other hand, from the viewpoint of constructing a fuel cell having the catalyst layer 21 in a semi-dry state, it is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less. Therefore, in the catalyst layer 21 in a semi-dry state, the content of the organic solvent in the coating film is preferably 1 to 20% by mass, more preferably 2 to 15% by mass with respect to water in the coating film. 3-10 mass% is further more preferable. As long as the content of the organic solvent in the coating film is within the above range, high fluidity of the ionomer 13 for entering the pores 14 can be obtained sufficiently, depending on the organic solvent used.

(Step of manufacturing a fuel cell having a semi-dry catalyst layer)
Step S13 is a step of manufacturing a fuel cell having the semi-dry catalyst layer 21 using the obtained semi-dry catalyst layer 21.

  A method for producing the fuel cell having the catalyst layer 21 in a semi-dry state is not particularly limited, and can be produced using a known method. For example, after the catalyst layer 21 in a semi-dry state is formed on both surfaces of the electrolyte membrane 1, the gas diffusion layer 22 is sandwiched between carbon paper or the like and thermocompression bonded, whereby the membrane electrode assembly 4 of the electrolyte membrane 1 and the electrode 2. Is obtained. Next, a fuel cell having a semi-dried catalyst layer 21 is obtained by sandwiching the outer surface of each electrode 2 between two separators 3.

(Step of applying voltage)
Step S14 is a characteristic step of the present invention, and is a step of applying a voltage to the fuel cell having the catalyst layer 21 in a semi-dry state.
By applying a voltage to the electrode 2 of the fuel cell having the catalyst layer 21 in the semi-dry state and applying a voltage to the catalyst layer 21 in the semi-dry state, the openings 15 of the pores 14 in the carbon support 12 are expanded. The average diameter of the opening 15 is increased. Further, since the catalyst layer 21 is in a semi-dry state, the ionomer 13 has high fluidity, and the ionomer 13 enters the pores 14 through the expanded opening 15 of the carbon support 12.

The step of applying a voltage is performed for the purpose of advancing the carbon oxidation reaction of the carbon support 12. The carbon oxidation reaction is an electrochemical reaction represented by the following formula.
C + H ₂ O = CO + 2H ⁺ + 2e ⁻ (1)
C + 2H ₂ O═CO ₂ + 4H ⁺ + 4e ⁻ (2)
It is the equilibrium potential ^E 0 = 0.52 V in the formula (1), the equilibrium potential ^E 0 = 0.21 V in the formula (2).
When the cathode potential is higher than the equilibrium potential E ^{0 in the} equations (1) and (2), the reaction proceeds in the oxidation direction, that is, in the direction of emitting electrons, and the carbon of the carbon support 12 is oxidized. In particular, when a phenomenon occurs in which a part of the cathode locally becomes an abnormally high potential at the start of the fuel cell, it is considered that the carbon of the carbon support 12 is mainly oxidized by the above formula (2). The present invention uses this carbon oxidation reaction to oxidize the carbon of the carbon support 12 and expand the average diameter of the openings 15 of the pores 14 of the carbon support 12.

  A method for applying a voltage to the fuel cell having the catalyst layer 21 in a semi-dry state is not particularly limited. For example, air or oxygen is supplied to the cathode, and hydrogen is supplied to the anode. A predetermined voltage is applied and held for a predetermined time. The voltage value to be applied and held is preferably 0.5 V or more, more preferably 1.2 V or more, and further preferably 1.3 V or more, from the viewpoint of promptly proceeding the carbon oxidation reaction. On the other hand, from the viewpoint of controlling the carbon oxidation reaction, it is preferably 2.0 V or less, more preferably 1.5 V or less, and even more preferably 1.4 V or less. Therefore, the voltage value applied and held is preferably 0.5 to 2.0 V, more preferably 1.2 to 1.5 V, and still more preferably 1.3 to 1.4 V.

  The voltage holding time is usually preferably less than 5 minutes, more preferably less than 2 minutes, although it depends on temperature, the amount of carbon support 12 to be subjected to carbon oxidation reaction, the degree of graphitization of the carbon support 12 and the like. is there. If the voltage holding time is too long, in addition to the carbon oxidation reaction, the chemical degradation of the electrolyte membrane 1 and the catalytic activity decrease, and the power generation performance of the fuel cell decreases.

  The application and holding of the voltage may be performed at room temperature (25 ° C.), but may be performed at a temperature not lower than room temperature and lower than 100 ° C., for example. By carrying out at a temperature of room temperature or higher and lower than 100 ° C., the fluidity of the ionomer 13 is improved.

  In addition to the above-described method of applying and holding the predetermined voltage, a potential cycle that simulates the start and stop of the fuel cell may be applied to the fuel cell. For example, with the nitrogen supplied to the cathode and the hydrogen supplied to the anode, the fuel cell is loaded with a potential cycle within a predetermined potential region. The potential region is preferably 0.5 V or more, more preferably 1.2 V or more, and still more preferably 1.V from the viewpoint of rapidly proceeding the carbon oxidation reaction with respect to the reference electrode (standard hydrogen electrode). 3V or more. On the other hand, from the viewpoint of controlling the carbon oxidation reaction, it is preferably 2.0 V or less, more preferably 1.5 V or less, and even more preferably 1.4 V or less. Accordingly, the potential region is preferably 0.5 to 2.0 V, more preferably 1.2 to 1.5 V, and even more preferably 1.3 to 1.4 V.

  The scanning of the potential cycle is not particularly limited, but scanning is normally performed for 1,000 to 60,000 cycles, with one cycle from changing from a low potential to a high potential to changing to a low potential again. The larger the number of cycles, the easier the carbon oxidation reaction proceeds, and the smaller the number of cycles, the easier it is to suppress chemical deterioration of the electrolyte membrane 1 and a decrease in catalytic activity. From the viewpoint of promoting the carbon oxidation reaction, the number of cycles can be increased, and from the viewpoint of suppressing the chemical deterioration of the electrolyte membrane 1 and the decrease in the catalytic activity, the number of cycles can be reduced.

(Step of manufacturing a fuel cell)
In step S15, the fuel cell having the semi-dried catalyst layer 21 is dried to completely remove the solvent in the catalyst layer 21, and the catalyst 11 supported in the pores 14 of the carbon support 12 is replaced with the ionomer 13. This is a step of obtaining a fuel cell having the catalyst layer 21 covered with the above. Although a drying process is not specifically limited, For example, the method similar to the drying method in step S12 which forms the catalyst layer 21 of the semi-dry state mentioned above can be used.

<Embodiment 2>
Next, a method for manufacturing a fuel cell according to Embodiment 2 will be described.
The fuel cell manufacturing method according to Embodiment 2 shown in FIG. 5 is that the voltage application target in the step of applying voltage is not a fuel cell having the catalyst layer 21 in a semi-dry state but ink for a catalyst layer. Different from the manufacturing method of the first embodiment. Other methods are the same as the manufacturing method of the first embodiment.

  As shown in FIG. 5, the fuel cell manufacturing method according to Embodiment 2 includes step S20, step S21, step S22, step S23, and step S24. Hereinafter, each step will be described.

(Step of supporting catalyst layer and step of preparing ink for catalyst layer)
Step S20 is a step of supporting the catalyst layer 21 and is the same as step S10 of the first embodiment. Step S21 is a step of preparing the ink for the catalyst layer, and is the same as step S11 of the first embodiment. For this reason, description of step S20 and step S21 is omitted.

(Step of applying voltage)
Step S22 is a step of applying a voltage to the catalyst layer ink.
The method for applying the voltage is not particularly limited. Usually, the working electrode, the counter electrode and the reference electrode (standard hydrogen electrode) are immersed in the ink for the catalyst layer, and the voltage is applied between the working electrode and the counter electrode. Hold for hours. The voltage value to be applied and held is preferably 0.5 V or more, more preferably 1.2 V or more, and further preferably 1.3 V or more, from the viewpoint of promptly proceeding the carbon oxidation reaction. On the other hand, from the viewpoint of controlling the carbon oxidation reaction, it is preferably 2.0 V or less, more preferably 1.5 V or less, and even more preferably 1.4 V or less. Therefore, the voltage value applied and held is preferably 0.5 to 2.0 V, more preferably 1.2 to 1.5 V, and still more preferably 1.3 to 1.4 V. The voltage holding time is usually in the range of 1 minute to 24 hours, although it depends on the temperature, the amount of carbon support 12 to be subjected to carbon oxidation reaction, the degree of graphitization of the carbon support 12 and the like. The application of voltage may be performed at room temperature (25 ° C.), but may be performed at a temperature of room temperature or higher and lower than 100 ° C., for example. By carrying out at a temperature of room temperature or higher and lower than 100 ° C., the fluidity of the ionomer 13 can be enhanced. As described in Embodiment 1, the potential cycle may be applied to the ink for the catalyst layer.

(Step of forming the catalyst layer)
In step S23, the ink for the catalyst layer after voltage application is applied to the surface of the substrate selected from the electrolyte membrane 1, the resin sheet, the metal plate, and the like to form a coating film, and then the coating film is dried and applied. In this step, the solvent in the film is removed to form the catalyst layer 21.
Step S23 differs from step S12 of the first embodiment in that the solvent in the coating film is completely removed. The other points are the same, and the method for completely removing the solvent in the coating film can use the same drying method as in Step S12 of Embodiment 1, and thus the description thereof is omitted.

(Step of manufacturing a fuel cell)
Step S24 is a step of manufacturing a fuel cell using the catalyst layer 21.
Step S24 is different from step S13 of Embodiment 1 in that the catalyst layer 21 from which the solvent is completely removed is used. The other points are the same, and the method for manufacturing the fuel cell using the catalyst layer 21 can use the same method as step S13 of the first embodiment, and thus the description thereof is omitted.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 1 ... Electrolyte membrane, 2 ... Electrode, 21 ... Catalyst layer, 22 ... Gas diffusion layer, 4 ... Membrane electrode assembly, 3 ... Separator

Claims (8)

A method for producing a fuel cell having electrodes (2) on both surfaces of an electrolyte membrane (1),
The electrode (2) has a catalyst layer (21) containing a carbon carrier having pores, a catalyst and an ionomer,
A voltage is applied to the ink for the catalyst layer in which the carbon carrier, the catalyst, the ionomer and the solvent are mixed (S22), or the catalyst layer (21) formed using the ink for the catalyst layer, which is semi-dry Applying a voltage to the fuel cell having the catalyst layer (21) in a state (S14),
Manufacturing method of fuel cell.   The method for manufacturing a fuel cell according to claim 1, wherein in the step of applying the voltage, a voltage of 0.5 to 2.0 V is applied.   The method for manufacturing a fuel cell according to claim 1, wherein in the step of applying the voltage, a voltage of 1.2 to 1.5 V is applied.   2. The method of manufacturing a fuel cell according to claim 1, wherein the carbon carrier after the voltage is applied has an average diameter of openings of the pores on an outer surface larger than an average diameter of the pores.   2. The method of manufacturing a fuel cell according to claim 1, wherein in the step of applying the voltage, a voltage is applied to the fuel cell having the catalyst layer (21) in the semi-dry state. The ink for the catalyst layer contains water and an organic solvent as the solvent,
The catalyst layer (21) in the semi-dry state is a coating film formed by applying the catalyst layer ink on a substrate, and the content of the organic solvent in the coating film is the coating layer. The method for producing a fuel cell according to claim 5, wherein the content is 1 to 20% by mass with respect to water in the membrane.   The method for producing a fuel cell according to claim 6, wherein the organic solvent includes an alcohol having a boiling point lower than that of water. Further comprising supporting the catalyst in the pores of the carbon support (S10, S20),
The method for producing a fuel cell according to any one of claims 1 to 7, wherein the catalyst supported in the pores of the carbon support is coated with the ionomer.

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